If wet concrete is placed into a form for walls, columns, etc., and the wet concrete is left to harden as placed, the resulting concrete will be left with holes from air pockets or “air voids”. To insure that the concrete is consolidated without “air voids”, a vibrator, which sends out shock waves to push lighter trapped air up and out of the wet concrete, is used.
The vibrator generally consists of three parts: the head, flexible shaft, and power unit. The head typically consists of a tube which is sealed in the front with ball bearing and an eccentric inside driven by a flexible shaft. The flexible shaft and the attached vibrator head are driven by the power unit, which is typically an electric motor or gasoline engine. To vibrate the wet concrete, the head and shaft of the vibrator are lowered into the concrete mixture. The speed of rotation required for good consolidation is typically from 10,000 rpm to 12,000 rpm.
In the case of gasoline engine driven vibrators, the throttle setting determines the speed. Most throttles for operating engine driven vibrators are of the linkage-type, and include a pivoting lever which controls the engine through a cable. In known linkage-type throttles, the pivoting lever pulls the cable, which in turn linearly opens the throttle. To close the throttle, the pivoting lever loosens the cable, which in turn linearly closes the throttle. Typically, the lever, the pivot, and the cable are exposed.
During the consolidating (vibrating) operation, the wet concrete can splatter, and consequently, the operator's hands, which are usually both on the flexible shaft to hold and guide the vibrator (see FIG. 6), are covered with wet concrete. When the operator controls the throttle, the wet concrete on the operator's hands then gets deposited on the linkage-type throttle. If the wet concrete on the linkage-type throttle is not washed off at the end of the day, it will solidify and the resulting hardened concrete can inhibit the operation of the throttle and in particular, the hardened concrete can prevent the throttle lever from moving to the desired power setting (for example, 10,000 rpm-12,000 rpm required for good consolidation of concrete). This results in poorly consolidated concrete.
Furthermore, the linkage-type throttle allows the operator full control of the throttle and does not prevent the operator from operating at below the minimum speed of rotation (10,000 rpm) required for good consolidation. Thus, the operator may operate at below the desired power setting either unintentionally, or for personal reasons such as to lower the noise level.